The technology conventionally provided for illuminating a liquid crystal display device such as a mobile telephone or the like consists of a light guide plate that guides light emitted from a light source to a liquid crystal display device and a backlight device providing this light guide plate, that illuminates a liquid crystal display device from the rear.
FIG. 1 provides a perspective view, showing the external appearance of a conventional light guide plate. Light sources of light emitting diodes 2 are shown in FIGS. 1(a), (b) and (c). Here, the light guide plate 1 is made of a transparent material such as PMMA or polycarbonate or the like, and has a substantially flat, planar form. The light guide plate has an upper face constituting an exit face 3 and a lower face constituting a reflective face 4, while one of the side faces provides an entry face 5. The reflective face 4 has reflective elements 6 formed thereon that reflect light entering from the entry face 5 toward the exit face 3.
Light emitted from the light sources 2 enters the light guide plate 1 from the entry face 5 and is reflected at the reflective elements 6 formed on the reflective face 4, being deflected in the direction of the exit face 3, before being emitted from the exit face 3. The light guide plate 1 in which light entering from the entry face 5 comprising one of the side faces is emitted from the exit face 3 comprising the main face, is known as a side edge type and is widely used for mobile telephones and the like.
FIG. 2 provides a cross-sectional view depicting the usage of a conventional light guide plate and backlight device. The light guide plate 1 is disposed directly under the liquid crystal display device 7, such that the entry face 3 opposes the lower face 9 of the liquid crystal display device 7 with the optical sheet 8 disposed between that exit face 3 and lower face 9. Light emitted from the light emitting diodes 2 is incident to the light guide plate 1 from the entry face 5.
This light entering the light guide plate 1 from the entry face 5 is deflected at the reflective elements 6 formed on the reflective face 5 that opposes the exit face 3, reflecting upward in the direction of the liquid crystal display device 7 and exiting from the exit face 3.
Light exiting from the exit surface 3 of the light guide plate 1 enters the lower face 9 of the liquid crystal display device 7 via the optical sheet 8. This optical sheet 8 points the light exiting from the light guide plate 1 upward in the direction of the liquid crystal display device 7 such that the light enters the lower surface 9 of the liquid crystal display device 7 vertically.
A reflector 10 that reflects light emitted from the reflective face 4 is disposed at the side closer to the reflective face 4 of the light guide plate 1. The reflective surface of the conventional reflector 10 is a pure, mirror surface.